Thread: PVA glue creep

Yes that's glue creep. Likely due to the wet weather following a long dry spell and the two bits of wood behaving not quite the same. There is a fair chance it will happen again. Best chance for a good outcome is to get the panel sealed right after sanding. I think any of the PVAs can have this happen.
Regards
John

Yep, that's creep and there's not much you can do about it; even once it's sealed and polished I've seen it happen. It's one of the reasons I prefer PU for laminating; PU cures chemically and once it's done, that's it. PVA sets by the carrier solvent (being water) evaporating off, but it can re-absorb water from the air and creep.

I might get some PU glue to try.

Is it used the same as PVA - do I need to spread it out? I see that it expands/foams making me think its not necessary

Also, the TimbaTech PU15 - does that mean that if its not clamped within 15mins its too late?

Titebond 2 and 3 are designed for exterior use. They have greater flexibility when cured. You quickly notice it when scraping dried hard glue from a surface. The Titebond Original is much more crystal like, so much so that it often pings away from the surface and smacks me right in the eye! Titebond 2 and even more so Titebond 3 feel 'gummy' when cured because they are maintaining their flexibility. So as the timber moves, so does the glue. The gummy flexible glues squish and stretch. If you squish a rubber ball, the sides burst out. Same thing happens with the glues. When the two boards squish harder together, the glue bursts out of the surface creating the glue ridge lines.

You can sand off the ridge lines, and it may/probably will occur again. Eventually though after many cycles of removing the ridge lines, the glue no longer squishes and bursts out far enough to break the surface and you are left with a slight depression in the glue line itself. It's only noticeable under high gloss finishes or if you are really looking for it, knowing exactly what to look for and how to look for it.

Titebond original, or any of the other interior grade PVA's creep, but they don't creep very much and I've never noticed a glue ridge line from with titebond original.

Originally Posted by qwertyu

I might get some PU glue to try.

Is it used the same as PVA - do I need to spread it out? I see that it expands/foams making me think its not necessary

Also, the TimbaTech PU15 - does that mean that if its not clamped within 15mins its too late?

Yes, you should spread it out into a film that's just thick enough to be shiny. I recommend laying a plastic sheet or glad wrap over your bench, the foaming can get pretty messy until you get the feel for how much glue you need. Also, DON'T try to wipe off any wet squeezeout, you'll just make more mess and push the glue into the grain, wait until it's dry and scrape it off with a blade. Wet glue can be cleaned with acetone. For minimum cleanup, mask around the joins with tape and pull the tape off when the foam forms a firm skin but still feels "foamy" (yields to pressure, but doesn't completely collapse). This is also the best time for cleaning internal corners with a chisel or scraper; these are absolutely fantastic for controlled scraping: https://www.japanwoodworker.com/prod...ne-akio-uozumi Carbatec used to sell them, but no longer

The TimbaTec PU numbers indicate the minimum clamp time, ie. PU15 can be taken out of clamps after 15 mins. Those clamp times are only good for an initial cure, if you pull them out that early the joins still should not be put under any stress for a few hours; we used to go with 4x minimum time for a working cure, so 1 hour for PU15 and 4 hrs for PU60. The data sheets are on their website for exact times, but you have roughly 2-3 mins working time with the PU15 and 6-8 mins with PU60, so make sure you have everything in easy reach and your clamps pre-set.

So with PU60, you wouldnt flip over the table to scrap the squeeze out until after 4 hours yeah? I never know what is considered 'stress'. Is the weight of a table too much stress?

Got any recommendations on where to get a big roll of plastic? or is waxed paper suitable too? (I would like to reuse the paper and roll it back up, and only cut it off once really messy)

I suppose it would be good to line the clamps too? Or will the plastic just spread the glue everywhere all over the timber? Is masking tape adequate to protect the clamps? Or is something like duct tape better (ideally I dont want to be re taping the clamps every time).

I also never quite worked out what counts as stress. For flat panels it's easy enough to scrape the glue when it's dry, so we just left it until we pulled it out of clamps.

A cheap tarp is good for glue-ups. When dry, the glue just pops off plastic, so you can reuse the tarp easily. A wire cup wheel on an angle grinder is good for cleaning clamps. If you're really precious about keeping them nice and shiny I guess you could line them...